1. Field of the Invention
This invention relates to apparatus for moving a bakery pan in an efficient fashion past a position where rows of dough packets are deposited in individual cavities or pockets in the pan. In particular, the invention relates to a variable speed indexing apparatus that alternately slows and speeds the progression of the pan past the position at which the dough packets are deposited.
2. Background of the Invention
In the baking industry, baking pans move in a stepwise fashion past a device that provides dough packets. The pans include a number of rows of cavities or pockets for receiving the dough packets. The pans are positioned one after another in series, usually with a leading edge of one pan abutting the trailing edge of another. Frequently, the type of bakery product being manufactured varies and the configuration of the pans used must be changed. For example, when making hamburger buns, the pans include rows of round pockets, and when making hotdog buns the pans include rows of oblong shaped pockets. The individual pockets include a leading edge and a trailing edge with individual pockets and are spaced apart from each other in the direction of pan travel.
The soft dough packets make it somewhat difficult to drop straight rows for deposition into corresponding rows of pockets in each pan. That is, after being divided into individual dough packets, transverse rows of dough packets translate through a mechanized conveyor system and drop from an elevation above the moving baking pans. To insure that a complete transverse row of dough packets is received into a corresponding row of pan pockets, a pan conveyor indexing mechanism is typically used to stop a row of pan pockets underneath where the dough packets are dropped. One indexing mechanism is disclosed in U.S. Pat. No. 5,476,035 to Florindez which utilizes a conveyor belt having magnetic elements to attract the bottom side of the pans. A motor drives the conveyor belts and a clutch/brake mechanism operates to alternately stop and start the conveyor movement. A proximity sensor senses the individual pan pockets, wherein the motor is disengaged and the brake applied. A timing clock operates to release the brake and re-engage the motor. The conveyor belt thus moves in a stepwise fashion past the location where dough packets are deposited in the pan pockets.
As mentioned, the type of baked goods being produced changes without stoppage of the conveyance system. Such changes introduced different types of baking pans in sequence. At the transition between different types of baking pans, the spacing between transverse rows of pan pockets changes. In addition, sequential baking pans may not be touching, resulting in gaps therebetween.
FIG. 1 diagramatically illustrates several sections in the movement of a baking pan in the prior art indexing system. At the upper portion, sequential baking pans 20a and 20b travel to the left, with the associated magnetic conveyor not been shown for simplicity. Each baking pan has transverse rows of pan pockets spaced apart in the direction of pan travel. Thus, for example, baking pan 20a has pans P1 through P4, and a baking pan 20b has a at least a first row of pan pockets P5. Below the schematically illustrated baking pans 20 is a graph with the speed of the pans in inches/second on the Y-axis and time in 0.5 second intervals on the X-axis. A base speed of pan travel is set at approximately 20 in./sec. The base speed approximates the speed at which all dough packets would fall into the correct pan pocket if the dropping of the dough packets were perfectly in synch with the pan movement. In reality, as mentioned, a number of factors contribute to disrupt this synchronism. For example, different gaps G between pans and varied spacing S between rows of pan pockets create uneven distances between adjacent rows and thus vary the timing of when sequential rows reach the drop point.
To adapt to the uneven pan pocket row timing, a proximity sensor in the system senses the leading edge of each of the pan pockets as indicated at A1 through A5. A periodic timing signal every 0.5 seconds is also provided as indicated at B1 through B5. The timing signal is synchronized to the moment when a dough packet drops from an elevation above the baking pan, after which time the pan speed should then pick up. In some instances, a slight phase difference between the actual time the rows of dough packets drop and the timing signal may be desirable to improve efficiency. Nonetheless, the timing signals are evenly spaced apart the same period as the spacing between drops of dough packet rows.
With reference to FIG. 1, prior to the first row of pan pockets P1, the baking pans 20 travel at the base speed. A1 indicates when the proximity sensor senses the leading edge of pan pocket P1 (time t1). The clutch disengages and brake engages to momentarily stop pan travel at time t2. A short time later, the periodic timing signal B1 is received by the control circuitry at time t3. This means a row of dough packets is dropping. At this point, the brake disengages and the clutch engages to begin ramping up the pan travel speed to the original base speed at time t4. The pans continue to travel at the base speed until the leading edge of the second row of pan pockets P2 is sensed by the proximity sensor (A2). This sequence of stopping and starting is repeated for each row of pan pockets.
In an efficient mode of operation, the indexing mechanism of the prior art will exhibit a waveform as indicated at 24 characterized by a spike from the base speed to the lower speed when the leading edge of a row of pan pockets is sensed. This temporary reduction in speed of pan travel is all that is necessary to insure that the dough packets are received in the pockets. In actual operation, however, the trapezoidal-shape waveform, such as at 26, occurs just as frequently as the spikes 24. In other words, the pans pause underneath the location at which the dough packets are dropped for a longer time than is necessary. This introduces an inefficiency in the overall throughput of the system. Moreover, the indexing mechanism of the prior art is limited in its capacity to adapt to different frequencies of pan pockets.
Another problem with the prior art indexing mechanism is the wear inherent in the mechanical components. The repetitive stopping and starting may cause eventual breakdown of the motor/clutch/brake drive system, or one of the components thereof. More problematic is the wear imposed on the gear train. Every time the gear train stops there is some backlash when the motion of the meshing components reverses. Continual backlash eventually wears the expensive gear train.
Although the indexing apparatus of the prior art generally work well to insure that a complete row of dough packets is received into each row of pan pockets, the constant stopping of the bakery pans slows down the overall efficiency of the system. Furthermore, the motor/clutch/brake drive mechanism eventually wears down and must be replaced. There is thus a need for an efficient conveyor system which requires less maintenance and lasts longer.
Such prior art indexing apparatus could employ stepper motors which are of the brushless-high rpm type that can be driven in a stop-start mode without many problems as opposed to a regular AC motor. A vector controlled drive may be designed to make a pattern by stopping and accelerating "ON" and "OFF" constantly without overheating the motor. A vector controller controls the pattern of timing and sequencing of the stepper motor by its programmed logic in its inboard programmable logic controller. But the overall cycles per minute of the stepper motor is not unlimited. In contrast, using the present invention which employs an AC inverter, the number of cycles is virtually unlimited.